Pulse modulation system



May 12, 1953 G. J. E. GOUBAU PULSE MODULATION SYSTEM 2 Sheets-SheetfiFiled May 25, 1951 U A .8 MW TG E e R VJ E NG r T W 0 W F. M G 1/ in W WM u m G Y LMW H u m E FG D G N E L AR 6 LU M U0 DS 00 O M M R wm C M y1953 cs. J. E; GOUBAU PULSE MODULATION SYSTEM Filed May 25, 1951 2Sheets-Sheet 2 INVENTOR- GEORG J.E GOUBAU BY f %//ome q Patented May 12,1953 smrrzs. PM

BTJESE'-MODULAT-ION- SES-TEM Geulfg'ifll. E. Gtuliau; lz'ong Brawn-,N;.J., assignor t'tr tlieflnitedi' State's of America" as representedliy'tlie .secmtiliytcffthe Army Alpnlicat'icn vMtty- 25;. 1951, SerialN05; 228,349

(er-anteatunaermitle 35,1 1. st code (1952a,- s'ec. 266) GlitiinssTherinvention describeetin;thefbllowirrgspeek fication? andclaims mayb'eamesnufacturedt used by or. for: the: Government iongovemmentafilpurposes; withoutthe payment? tot me at an royalty thereon.

This inventionmelates to a? puiseteeneretorsys'r tem and?moreparticularly tot: as modulated z 191515 genera-tor systmnxhavingvmeans for moduletmg; the frequency or rate of1occurrence:-ofthe generated pulses in acccrclanee with modulating; potentials;

It has been. proposed to trernsrnit intelligenee in the form of a trainor pnlsest spaced? apart according: to" a: functionof the:- a-mplitudeof a modulating voltage: \trhich matt'represent the intellig'en'ce t0-be transmitted; Heretofcre such systems have not proved; practical: forusenvittr portable" ecmipmentbecause-someform. of syn chronizationbetween-2 the transmitter: and: the demodulator was required: 1

It lsan object! on the presenttinventicn thererfore; to provide" aan;i-mprcvedv and simplified-pulse modulation-systemwherein'nofisynehronizetion is; required.

It is a further object nixthemresent -inventlonl to: enable thegeneration of pulses whoseapulse rate can be frequency,-modulated-1imaccordance with theme tlnleting-voltage.

It is: still a-- further objectoi: the present; invention. to provide a,pulse generator system whereinthe. nulsc frequency or-ratect recurrenceof the generated pulseswaries in -inverse rnoncrw tion to. themedulattng voltaget- In accordance with the embodiment oil-the presentinvention to" be describedhcreinwat sinuw soidtvoltage- 0t varyingfrequency,-. for: example the output ot. a voice micrcphone iscaused.tofl modulate the outputof. a sawstccth generator; circuit so that theamplituderlevel or. charging. peried, of the. sawrtooth Waves is sufistanti allyt proportionaltto the amplitude of the. modulatmg;

voltage. At. the endtot eaotLcliarging periodta pulse is. generated,thus producing; a. trei'n of. pulses havinga frequencywhichwvani'e'stminverse proportion to the amplitude ofiTthemodulhtingtvoltagee These pulses are. applied. to a) pulse.

tbett'i generator: circuit :t.

Zv required pulse amplitude for operatingtfie sat-w tc'otli circuit; I

For a; Better understanding; of the" present iii-- vention, togetherwith other and'fnrther objects refereneeis had" tothefollewingdescripticni taken in eonnectien Wi-tH- tk'ie accompanying di'awifigs, in wfiicha I Eigiure 1 is block diagram of 2: pulse generatbrsysteminaceorclttnte withinvention;

figure 2 2' illustrates" tte distal-lent circuits of the system cfFigure-l' an'd Figure inclizcles 2t series of graphs utilized inexplaining the operzttion': of the fi igure fi akrreenge mentl..

Referring now to? Figure?" l of the drawings; there is shownsaxpu'lscigenerator system for gen ere-ting; a l'tu'etlitgn oftime'esp'scedt pulses: Havingw frequency Whicln varies: int/el teproportion tofithe amplitude ozttlie m oizle-tim-voltttgea 'Z'Ch'e"system' includes" a, saw-te0th gen tori circuitfl for deriving; a m-nearvoltage of s t WOUUHIWQJVEF' form: havin a; nes-itive' slope: saw-toothvoltege islcombinetl with themcctuletien:voltage? derived from: source:t in mcduizttlne cirm'nt 55 which determines the amplituii'elevenonlineairi' emerging; per iedmf the SitW-tOOtHVflltIgt-XModmatting: circuit it includes: means for: generating? tire:tsientIcurrent puise when v 'e" amplitude levekoft the sew-toath voltageleztcltesthemodu lation voltage: The: transient cutput of modw' lating 1circuit 5- isapplietl; to pulse "forming f circuit- 8 for generating.constant width: pulses of short dnmtiom the. end of each chargingperiod; These. pulses are usedttoth for medulatingt'rans rnttter M7,and, throng-h the medium of" delay- 0 um t rior terminatingthechargizm;v per-tottsothat the cyclevmay 'be repeated.

Figure ZQSEOWS the circuit diagram" for the system of Figure 1 Vacuumtubes M :5 and i8 and their associated: circuits-:- comprise sew The sawtooth. vc'tt' I acrosscapacitor: it connected between. plate 5 of.SHAW-13801711 genera-tor tube it andgr'oundf Tate is connectedtQ-wpesttive source of potential. 3+, which may be: provided age isclevelope 5 in the conventional" manner, through series"v cam formingcircuit whose. purpose is to. shapetlie pulse to a shape optimumfor theoperating: of' altransmitten. Theloutputdrom the pulse-form! ing=circuitis used. both-formotlu1ating-the trans. mitter, and through I themedium. of: a delay-l line: for terminatingthe period/of-thesaw-tooth't-wasve sothat th e saw-toctlt genemtor: circuit! may: proceed througl-l another: cyclerl The delayi'linerprd nect'ed 'resistorsizand Tillie i 6 is self-biasect byg'the parallel arrangement cit-resistoramt capacitor 2'8 connected" Between cathoeie 331 of: tube: Fanflground.

Tcobtainfa; linear saw tooth' rise with a positive slope a"conventional" boct-st1ap cathode ftllower circuit is provided: Assnownyth'e 52; tooth voltage elveltin'ed across" capacitor [8 1samplieditc grid oficaithcde'fcl'lcwer I8. The

v iclesa delayintervat suffieient tw develop the 55v outputft'mnroath'ofle 34* of tub lfgy a the junction of series connectedresistors 22 and 24 through coupling capacitor 35. The normally constantvoltage at the positive end of resistor 22 has thus superimposed upon itthe rising voltage on charging capacitor 19 so that the voltage dropacross resistor 22, and hence the charging current, is maintainedpractically constant.

As will hereinafter he explained, saw-tooth generator tube Iii iscontrolled by pulses which are applied to grid 38 of tube 15 by means ofcathode follower I4 and coupling transformer 46. These pulses areapplied to grid 4| of cathode follower tube M from the output of delayline l2 and the consequent pulses developed across cathode resistor 42of tube [4 are applied to primary winding 44 of transformer 48 throughcapacitor 45. As shown, the free end of primary winding 44 is connectedto ground. Secondary winding 48 of transformer 48 is connected betweengrid 38 and ground. Plate 52 of cathode follower tube 14 is connecteddirectly to-B+.-

The windings of transformer 48 are poled so that -there is no polarityreversal of signals ap plied to its primary winding.

The linear saw-tooth output voltage developed across capacitor I 9 isapplied to grid 54 of vacuum tube 56, which, together with vacuum tube58 and its associated circuits comprises modulating circuit 6. Cathodes60 and 62 are connected to ground by common cathode resistor 64. 66 oftube 56 is connected to B+ through series connected resistors 68 and 10.Plate 12 of tube 58 is connected directly to B|. Because of the voltagedeveloped across common cathode resistor 64 due to the plate currentdrawn by tube 58; tube 56 is normally biased to cut-off. Capacitor BI isconnected between the junction of plate resistors 58 and 18 and groundto effectively reduce the plate voltage applied to plate 66 to arelatively low value. Thus, by this arrangement, tube 55 will berendered transiently conductive only when the amplitude of the sawtoothvoltage applied to grid 54 is great enough to overcome the biasdeveloped across common cathode resistor 64.

As shown, audio modulating voltage is applied to grid 14 of tube 58 bymeans of audio coupling transformer 16. It is to be understood of coursethat any other suitable coupling means may be used. The plate current oftube 58 is thus controlled by the audio modulating voltage to develop abias voltage across common cathode resistor 64 which is proportional tothe amplitude of the modulating voltage. When the linearly risingsaw-tooth voltage developed across capacitor I9 reaches an amplitudesufiicient to overcome the bias voltage across resistor 64, capacitor I9is effectively connected across the grid-cathode circuit of tube 56 andis thus rapidly charged by grid current to a steady state voltage.During this period, tube 56 may be said to be transiently conductive andthe transient plate current thus produced generates a negative voltagepulse in the plate circuit thereof.

The output from plate 66 is capacity coupled to grid 18 of amplifiertube 88, which together with pulse forming tube 82, comprises pulseforming circuit 8. The output of amplifier tube 85 is capacity coupledto grid 84 of pulse forming tube 82. The anode load of tube 82 includesa pulse shaping network comprising inductance 8B shunted by resistor 88.Cathode 90 of tube 82 is connected to ground through resistor 92. Theoutput of cathode 90 is applied to grid 4| of tube I4 through a suitabledelay line l2 which Plate provides a sufiicient delay to permit thevoltage developed across cathode resistor 92 to reach an amplitudecapable of operating the saw-tooth generator circuit.

The curves in Figure 3 clearly illustrate the operation of the pulsegenerator described. In this figure, curve A represents an exaggeratedportion of the modulating voltage from source I At time n, the amplitudeof the saw-tooth voltage has reached the amplitude of the bias voltage,and, at this instant, tube 56 is rendered conductive. Capacitor I9 isthus connected in the grid-cathode circuit of tube 55 and is now chargedby grid current flowing in the gridcathode circuit. As a result, thevoltage across capacitor l9 reaches a steady state value at time 152.The period ti-tz may be designated as the transient period and currentin the cathode-plate circuit of tube 56 during this period may be termedthe transient current. As explained above, a relatively short transientperiod is provided by reducing the voltage applied to plate 65 to arelatively low value.

Curve C illustrates the negative pulse developed at plate 66 during thetransient period. It may be assumed that the transient period forsuccessive saw-tooth waves is substantially constant, thusproviding atrain of constant width negative pulses. The negative pulses illustratedin curve C are amplified in tube 80 and the am plified positive "outputpulses from said tube are applied to pulse forming tube 82. The outputof the plate circuit of tube 82 is represented by curve D and may beapplied through suitable shaping circuits to pulse a transmitter.

Curve E represents the positive output pulse developed across cathoderesistor 92 during the transient period which is applied to the inputcircuit of delay line l2. The interval T represents the amount of delayprovided by delay line E2. The output of the delay line, illustrated incurve F, is applied to grid 4| of tube I4. The cathode output of tube 14is thus applied to primary winding 44 as a positive pulse. Since therevis no reversal of, polarity through transformer 40, the positive pulsesshown in curve F are also applied to grid 38 of saw-tooth generator tube16 through secondary winding 48. It is to be assumed that when thepulses applied to grid 33 reaches an amplitude represented by the lineK, saw-tooth generator tube 16 is triggered. to discharge capacitor I 9,and, consequently, the cycle is repeated. It is to be understood, ofcourse, that by merely adjusting the delay interval T, the discharge ofcapacitor 19 may be,

made to occur at any convenient time after the steady state voltage hasbeen reached.

For increasing amplitudes of modulating volt age, it is apparent thatthe charging period tO-tl will be proportionally increased and, fordecreasing amplitudes of audio voltages, the charging period td-ti willbe proportionally decreased. Thus, the output of pulse forming tube 82comprises a plurality of time-spaced pulses having a frequency, or rateof occurrence, which modifications as fall within the true spirit andscope of the invention.

What is claimed is:

I 1. A pulse generator system comprising, in combination, means forgenerating a periodic voltage of saw-tooth waveform, a source ofmodulating voltage, means connected to said modulating voltage and theoutput circuit of said sawtooth generating means for combining saidsawtooth voltage and said modulating voltage whereby the amplitude levelof said saw-tooth voltage is substantially proportional to the amplitudeof said modulating voltage, a pulse forming circuit connected to theoutput of said last mentioned means for generating signal pulses havinga frequency which varies in inverse proportion to the amplitude of saidmodulating voltage, said pulses being generated at a periodcorresponding to the peaks of said saw-tooth voltages, and a delay lineconnected between said pulse forming circuit and the input circuit ofsaid generating means to terminate the period of said saw-tooth voltagea predetermined time after the initiation of said pulses.

2. A pulse generating system comprising, in combination, means forgenerating a voltage having a saw-tooth waveform of positive slope, asource of modulating voltage, means for modulating said saw-toothvoltages in accordance with said modulating voltage whereby theamplitude level of said saw-tooth voltage is substantially proportionalto said modulating voltage, means for generating pulse signals at thepeaks of said saw-tooth voltage, said pulses having a frequency whichvaries in inverse proportion to the amplitude of said modulatingvoltage, and a delay line connecting said last mentioned means and saidsaw-tooth generating means to terminate the period of said saw-toothvoltage a predetermined time after the initiation of said pulse signals.

3. A pulse generator system comprising in combination, an aperiodicsaw-tooth wave generator for generating substantially linear voltages ofsaw-tooth waveform, a source of modulating voltage, a normallynon-conducting vacuum tube connected to said modulating voltage sourceand said saw-tooth wave generator for combining said saw-tooth voltageand said modulating voltage, means for biasing said vacuum tube inaccordance with said modulating voltage whereby the amplitude level ofsaid sawtooth voltage is substantially proportional to the amplitude ofsaid modulating voltage, said vacuum tube being rendered transientlyconductive only when the amplitude of said saw-tooth voltage reaches theamplitude of said modulation voltage, means responsive to the transientcurrent in said vacuum tube for generating pulses having a frequencywhich varies in inverse proportion to the amplitude of said modulatingvoltage, and delay means connected to said last mentioned means and theinput circuit of said saw-tooth wave generator for terminating saidsaw-tooth voltage period a predetermined time after the initiation ofsaid transient current.

4. A pulse generator system comprising a sawtooth wave generator forgenerating substantially linear voltages of saw-tooth waveform having apositive slope, a source of modulating voltage, a first vacuum tube,normally non-conductive, having at least a grid, a plate, and a cathode,a second vacuum tube having at least a plate, grid, and cathode, thecathodes of said first and second tubes having a common cathoderesistor, the

grid of said first tube being connected to the output of said saw-toothgenerator, the grid of said second tube being connected to saidmodulating source whereby said first tube is biased in accordance withsaid modulating voltage to control the amplitude level of said saw-toothvoltage, said first vacuum tube being rendered transiently conductivewhen the amplitudes of said modulating voltages and said saw-toothvoltages are substantially equal, means connected to the plate of saidfirst tube responsive to the transient current for generating signalpulses having a frequency which varies in inverse proportion to theamplitude of said modulating voltage, and delay means connected betweensaid pulse generating means and said saw-tooth generator to terminatethe period of said saw-tooth voltage a predetermined time after theinitiation of said transient current.

5. A pulse generator system comprising in combination means forgenerating aperiodic voltages of substantially saw-tooth Waveform, amodulating voltage source, means connected to said generating means andsaid modulating source for combining said saw-tooth and modulatingvoltages whereby the amplitude level of said sawtooth voltage iscontrolled by the amplitude of said modulating voltage, means connectedin circuit with said combining means for generating voltage pulses whenthe amplitudes of said modulating voltage and said saw-tooth voltage aresubstantially equal, and delay means connected to said last mentionedmeans and said saw-tooth generating means for terminating the period ofsaid saw-tooth voltage a predetermined time after the initiation of saidvoltage pulses.

6. The pulse generator system defined in claim 4 wherein said pulsegenerating means comprises an amplifier having its input circuit coupledto the plate of said first vacuum tube, a third vacuum tube having atleast a grid, plate, and cathode, the grid of said third tube beingcoupled to the output of said amplifier, the cathode of said third tubebeing connected to said delay means, and a pulse shaping network incircuit with the plate of said third tube.

7. The pulse generator system defined in claim 6 wherein said pulseshaping network comprises a resistor and an inductor connected inparallel.

GEORG J. E. GOUBAU.

Name Date Edelsohn Mar. 13, 1951 Number

